When the nature and performance of tires for trucks, passenger cars, and other vehicles are measured, one of important measurement items is rolling resistance of the tire. The rolling resistance of the tire is a tangential force acting between the tire and the ground. In a rolling resistance testing machine, the rolling resistance is measured as a force Fx (a change in rolling resistance Fx when a pressing load Fz is changed) that acts between a testing tire and a simulated traveling road surface such as a drum in a tangential direction.
A method based on a drum type rolling resistance testing machine is representative of a method of measuring the rolling resistance Fx. The drum type rolling resistance testing machine is configured to bring a tire into contact with a simulated traveling road surface formed on an outer circumference of a traveling drum in a pressed state, and to measure a relation between the pressing load Fz and the rolling resistance Fx using a multi-component force detector (load cell) provided for a spindle supporting the tire.
To be specific, when the rolling resistance Fx is measured, a load fx is measured in a rolling resistance direction by the multi-component force detector provided for the spindle, and Fx can be calculated (load method) by “Fx=fx(L/Rd)” where Rd is a radius of the traveling drum, and L is an interaxial distance between the traveling drum and the tire spindle. Further, as another method, there is also a method (torque method) of measuring drive torque τ for rotating the traveling drum and measuring the rolling resistance Fx by “Fx=τ/Rd.”
Incidentally, in such a rolling resistance testing machine, it is necessary to calibrate the multi-component force detector at the time of using the testing machine. In addition, when the multi-component force detector is continuously used over a long time, an error in a detected value occurs. As such, the multi-component force detector needs to be calibrated, for instance, at every fixed time.
As a method of calibrating the multi-component force detector, various methods are developed. However, as illustrated in Patent Document 1, there is a method of performing calibration after a test load is applied in each direction using a weight whose mass is known. Further, as illustrated in Patent Documents 2 and 3, a method of performing calibration by providing an external force via a high-precision load tester is also disclosed.